ALLOCYCLIC CONTROLS ON LATE QUATERNARY SEDIMENTATION IN THE EASTERN GULF OF SANTA CATALINA, OFFSHORE SOUTHERN CALIFORNIA

COVAULT, Jacob A., Department of Geological and Environmental Sciences, Stanford Univ, Stanford, CA 94305-2115, [email protected], NORMARK, William R., US Geol Survey, 345 Middlefield Rd, Menlo Park, CA 94025-3591, and GRAHAM, Stephan A., Department of Geological and Environmental Sciences, Stanford Univ, 450 Serra Mall, Bldg. 320, Stanford, CA 94305-2115

Extensive high-resolution deep-tow boomer seismic-reflection profiles and sediment cores provide the opportunity to assess late Quaternary sedimentation within the eastern Gulf of Santa Catalina (eGoSC). eGoSC is a turbidity current-fed, structurally active, open California Borderland basin. The primary sediment contributor to eGoSC is the Newport Canyon-channel system, which has multiple canyon heads located near the eastern edge of the Long Beach Shelf. The San Pedro littoral cell, San Diego Creek, and Santa Ana River delta are the predominant sediment feeders to the Newport system. Secondary contributors to eGoSC are slope gullies along its eastern side that receive sediment from coastal creeks that drain the San Joaquin Hills and Santa Margarita Mountains.

Cores from the floor and levee of Newport channel show turbidity current flows contributed to eGoSC during the late Pleistocene and continuing through the Holocene marine transgression. During marine transgression, multiple canyon heads developed on the Long Beach Shelf, probably because of fluvial system migration. Less prominent fluvial systems that fed the slope gullies were unable to keep pace with marine transgression, and as a result, the gullies were deprived of sediment. Some slope-gullies remain active in the modern, probably as a result of seismically-triggered turbidity currents along the Newport-Inglewood-Rose Canyon Fault Zone.

The evolution of the Newport Canyon-channel system reflects encroachment on the east from slope progradation. The bathymetric relief that narrowed eGoSC at its southern end may have formed above blind thrust faults. As a result, the multiple canyon heads coalesce >30 km south of the shelf edge. Immediately down system, a buried bathymetric ridge and slope gully sediment deflect flows to the west, extending the channel to the head of the San Diego Trough >30 km away.